History of Flight
On June 2, 2015, about 1520 central daylight time, a Sonex SA amateur-built airplane, registered as N123SX, impacted unoccupied, parked military vehicles at a manufacturing facility shortly after departing from the Wittman Regional Airport (OSH) in Oshkosh, Wisconsin. The private pilot and a pilot-rated passenger were fatally injured, and the airplane was substantially damaged. The airplane was registered to and operated by Sonex Aircraft LLC under 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed, and the flight operated without a flight plan. The local flight was originating at the time of the accident.
According to OSH air traffic control tower personnel, the airplane departed runway 9 from the intersection of runway 9 and runway 13. After clearing the airplane for takeoff, the tower controller focused attention on inbound traffic and did not witness the accident.
A surveillance video from the Oshkosh Defense manufacturing facility captured a portion of the accident flight. The video showed the airplane during its initial climb from the runway; in several frames, a wisp of white appeared to briefly emanate from the airplane.
Personnel Information
The pilot, age 40, held a private pilot certificate with ratings for airplane single engine land, airplane single engine sea, and gliders. He was issued a third-class medical certificate on February 22, 2013, without limitations. As of March 15, 2015, the pilot had accrued 715 hours of total time, with an estimated at least 540 hours in Sonex-type airplanes and 25 hours in the AeroVee Turbo airplane.
Aircraft Information
The Sonex SA was a low-wing, tailwheel, two-seat airplane built in 2007, serial number 0008. It was powered by a 100-horsepower AeroVee Turbo engine driving a wood composite, fixed-pitch Sensenich propeller. On June 20, 2007, it was issued a special experimental/amateur-built airworthiness certificate. The original AeroVee engine was removed, and the company's prototype AeroVee Turbo was installed on May 8, 2014, returning the airplane to FAA Phase 1 test flight period at a tachometer time of 96.52 hours. Phase 1 was completed on September 23, 2014, at 118.2 hours. The last recorded maintenance was a modification to cockpit avionics on January 12, 2015, at a tachometer time of 126.8 hours. Following that, the airplane was flown cross-country to Florida and returned to Oshkosh on April 28, 2015. A company mechanic recalled flying with the accident pilot for no more than 1 hour in the days preceding the accident and stated the flight was uneventful.
The airplane was last fueled on April 28, 2015, at De Kalb Taylor Municipal Airport and flown about 125 nautical miles to Oshkosh.
Meteorological Information
At 1537, the automated weather reporting facility at Wittman Regional Airport reported wind from 130° at 11 knots, visibility 10 miles, clear sky, temperature 72°F, dew point 39°F, and an altimeter setting of 30.10 inches of mercury.
Wreckage and Impact Information
The accident site was located about a quarter mile east-northeast of the departure end of runway 9. The airplane came to rest on a general heading of 220 degrees on unoccupied parked military vehicles on Oshkosh Defense property. All components were found in the immediate vicinity. The engine separated and was located on the ground in front of the airplane. All major components remained attached. The airplane was transported to a secure facility for examination.
Both wings displayed impact damage. The left wing leading edge was twisted rearward; the outboard portions of the left aileron and wing were torn and separated. The right wing leading edge had rearward accordion crushing. The empennage was distorted and wrinkled near the aft cockpit but relatively undamaged near the rudder. Horizontal and vertical stabilizers and rudder were undamaged; both elevators were buckled at their inboard sides. Flight control continuity was established from ailerons to a section under the cockpit control stick; elevator continuity was established similarly. The area was crushed, preventing smooth movement of cockpit controls. Rudder continuity was established to the rudder pedals. Flaps appeared retracted; the flap selector bracket was deformed, and the flap handle was bent away. Both throttles were in the full forward position; the mixture control was near idle-cutoff with a witness mark. The elevator trim was near full nose down, which, according to the company, was normal for takeoff. No preimpact anomalies were detected with the airframe.
The propeller remained attached to the engine; both tips were fractured aft. Gouges were on the propeller nose cone, but no rotation scoring was detected.
The AeroInjector carburetor was impact separated from the engine but remained connected via cables. The intake housing to the turbocharger was impact separated. The cylinder rocker box over No. 3 and 4 cylinders was also separated, with rearward distortion of rocker arms and rod housings. Engine and valve train continuity were confirmed. Seven of eight spark plugs were examined; none were excessively gapped or fouled. The top No. 1 spark plug was not removed due to being bound. Oil was present throughout. Cylinders had normal wear and deposits. The AeroInjector throttle slide operated smoothly, and the needle valve was properly oriented and unobstructed.
The turbocharger could not be rotated by hand. Disassembly revealed static marks on compressor blades without smearing or deformation, and a crack in the bearing housing. Disassembly was halted, and the component was sent to the NTSB materials laboratory.
Medical and Pathological Information
An autopsy performed on the pilot by the Fond du Lac County Medical Examiner listed the cause of death as multiple traumatic injuries. The FAA Civil Aerospace Medical Institute performed forensic toxicology; testing was negative for carbon monoxide and ethanol. Ibuprofen was detected in cavity blood, a non-narcotic analgesic and anti-inflammatory agent.
Tests and Research
The turbocharger was examined at the NTSB materials laboratory. Sonex did not provide manufacturer information but provided an exemplar assembly. Impact marks on the compressor housing were consistent with little relative motion between blades and housing at impact. Six compressor blades had radial cracks with deformation. The compressor and turbine wheels turned freely together within the center housing. The flange attaching the center housing to the compressor housing was fractured uniformly, consistent with overstress. The fracture location indicated movement of the compressor housing to the right relative to the center housing.
The accident wastegate actuator was shipped to Sonex for functional testing on a test cell engine. The accident engine could not be used. The actuator was installed on a test bed engine; under NTSB and FAA auspices, the engine was started and run to maximum power. The wastegate opened when manifold pressure exceeded 43 inches and maintained 40 to 43 inches. Engine RPM was generally about 3,100. When the wastegate actuator was opened, engine produced about 2,500 RPM with manifold pressure 28 to 29 inches. Attempts to replicate white smoke production using full range of mixture motion and speeds, including simulated water intrusion, were unsuccessful. Actual engine performance with a seized turbocharger could not be conducted. A company employee reported a degraded turbocharger a few weeks earlier; that turbo was found partially seized, but examination of the accident turbo did not find a similar signature. Replicating a seized turbocharger during engine operation was not possible.
The accident engine was disassembled; no preimpact anomalies were detected.
The MGL Avionics iEFIS Lite micro SD card contained no flight performance data for the accident or prior flights. Only GPS coordinates and altitude were retrieved from the iEFIS, but without time information, so performance could not be evaluated. The available data showed the recording began near the intersection of runways 9 and 13; the airplane departed near taxiway alpha, climbed to about 100 feet above ground level, leveled off, turned left over railroad tracks at the end of the runway, and began a descent, at which point the recording ended.